Recently developed organic electro-optic materials have demonstrated large increases in activity creating a drive towards utilizing organics in ring micro-resonators and modulators. These materials allow for extremely low drive voltages and fundamental response times within the terahertz region. Present synthetic efforts have efficiently incorporated molecules with large first molecular hyperpolarizabilities, β, into macromolecular systems producing unprecedented electro-optic coefficients, r33. Previously, incorporation of these large β molecules into macromolecular systems proved difficult due to phase separation or molecular aggregation within the processed films. Therefore, integration into workable devices was inconsistent and difficult. The new material systems however, have shown considerably enhanced film qualities, leading to improved device incorporation and fabrication. This paper will focus on current organic materials strategies and their incorporation into current ring micro-resonator devices and results.
This communication primarily deals with utilizing organic electro-optic (OEO) materials for the fabrication of active wavelength division multiplexing (WDM) transmitter/receiver systems and reconfigurable optical add/drop multiplexers (ROADMs), including the fabrication of hybrid OEO/silicon photonic devices. Fabrication is carried out by a variety of techniques including soft and nanoimprint lithography. The production of conformal and flexible ring microresonator devices is also discussed. The fabrication of passive devices is also briefly reviewed. Critical to the realization of improved performance for devices fabricated from OEO materials has been the improvement of electro-optic activity to values of 300 pm/V (or greater) at telecommunication wavelengths. This improvement in materials has been realized exploiting a theoretically-inspired (quantum and statistical mechanics) paradigm for the design of chromophores with dramatically improved molecular first hyperpolarizability and that exhibit intermolecular electrostatic interactions that promote self-assembly, under the influence of an electric poling field, into noncentrosymmetric macroscopic lattices. New design paradigms have also been developed for improving the glass transition of these materials, which is critical for thermal and photochemical stability and for optimizing processing protocols such as nanoimprint lithography. Ring microresonator devices discussed in this communication were initially fabricated using chromophore guest/polymer host materials characterized by electro-optic coefficients on the order of 50 pm/V (at telecommunication wavelengths). Voltage-controlled optical tuning of the pass band of these ring microresonators was experimental determined to lie in the range 1-10 GHz/V or all-organic and for OEO/silicon photonic devices. With new materials, values approaching 50 GHz/V should be possible. Values as high as 300 GHz/V may ultimately be achievable.
Future generations of flexible, transparent electronics will require the use of polymer based thin-film transistors (TFTs) exhibiting high carrier mobility. The problem of enhancing TFT characteristics is addressed in this report. We investigate the nanoscale, self-assembled monolayer (SAM) influence on organic-based thin film transistors (OTFT) at the interface between semiconducting polymer and both the source/drain metal contacts and the insulator. Capacitance-voltage (C-V) characteristics help to elucidate the role of SAMs in the OTFT structure and the charge injection mechanism. Positive trends and parasitic effects are also addressed in characterization.
Future generations of flexible, transparent electronics require the use of polymer based thin-film transistors (TFTs) with high carrier mobility. The problem of enhancing TFT characteristics is addressed in this report. Systematic studies were performed to optimize the thickness and composition of the active and dielectric layers. Different electrode materials were tested along with “top” and “bottom” device configurations. Various coating techniques (SAM) were applied to achieve a higher degree of order in polymer chains of semi-conducting layer. Results demonstrate the influence of the mentioned factors on the TFT performance, including increase of mobility and on/off ratio.
There is a considerable interest in the use of metal centered materials as a light source in the growing field of organic light emitting devices (OLED's). In these devices, a polymeric host matrix containing either a carbazole type polymer or polyfluorene derivatives is used to help facilitate energy transfer to the luminophore. We have shown that by using a gadolinium complex that consist of three equivalents of a chelated dibenzoylmethane b-diketone ligand and one equivalent of a phenanthroline type ligand as a component in the host matrix, the performance of a double layer type OLED is improved. We have studied OLED systems that contain tris chelated europium compounds that contain three equivalents of partially fluorinated β-diketone type ligands and an equivalent of a phenanthroline type ligand. In these devices, the external efficiency has shown a 30-fold increase. We have also shown there is an increase for Osmium based OLED's that use the gadolinium complex as part of the polymer matrix. In these devices, the maximum quantum efficiency increased from 2.1% to a value of 3.8%.
Future generations of photonic devices which incorporate poled organic nonlinear optical materials may be aided by, or require the use of non-traditional electrodes. This report details the integration of highly doped silicon as one of the poling/modulating electrodes in the simple reflection type experiment for determination of nonlinear optical activity in a guest-host polymer system. The measurements illustrate that the behavior of doped-silicon and the traditional indium tin oxide (ITO) electrodes are analogous. A number of organic chromophore guests were investigated as well as multiple polymer hosts. Results demonstrate both successful poling and subsequent modulation of NLO materials, including the calculation of r33 values comparable to those achieved using a standard ITO electrode.